Momentary electrical contact apparatus



July 30, 1963 A. BENNETT, JR 3,099,755

MOMENTARY ELECTRICAL CONTACT APPARATUS Filed April 7. 1960 Fig. 2A.

I A F g-3- PHASE PHASE /.PS2

SHIFTER SHIFTER I o e o f(1)P(t) f L/ cjflfd C PRI 1N, VRSl L 1/ o VRS2 f T I I EN T Fig.4. 1

PHASE /PS3 PHASE PSI' SHIFTER SHIFTER fH) PH) PRI 1 I ma K IINVENTOR WITNESSES M Allen LBenneH, Jr. mf a ATTOR United States Patent 3,ll,755 MQMENTARY ELECTRICAL CONTAQT AllARATiJfl Allan I. Bennett, In, Franklin Township, Westmoreland County, Pa, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsyl- Vania Filed Apr. 7, 1960, Ser. No. 28,713 12 Claims. (Cl. 307-113) The present invention relates generally to momentary electrical contact apparatus and more particularly to momentary electrical contact apparatus for making, at periodically recurring intervals, an electrical contact of short time duration, ie. of time duration short compared to the interval between contacts.

In many applications the need frequently arises for making at periodically recurring intervals an electrical contact, the time duration of electrical contact being extremely short compared to the interval between successive establishments of the electrical contact. Such apparatus usually requires the contact resistance to be low and constant when electrical contact is established and the time of occurrence and the time duration of the electrical contact must be quite stable. Further requirements generally are that the electrical contact is to have no internal generated voltages, or at worst only small and constant ones, and finally, a high impedance is required between the contact terminals when the electrical contact is open.

A mechanical device used in such apparatus is the vibrating reed type switch. Such a switch requires only a stationary coil for energization; the reed stationary at one end, vibrates as a cantilever beam, operating a set of contacts which may include the reed itself. The only motion other than the flexing of the reed is the relatively slight flexing of the contacts, resulting in an assembly of rather long life. Through the use of proper contact materials the contact resistance and generated voltage may be made quite low, and with suitable insulation the open circuit resistance may be made very high. It is, however, difficult to obtain stable, short duration electrical contacts. Conventional apparatus obtains a momentary electrical contact between the reed and a flexible contact by adjusting the flexible contact away from the vibrating reed contact to a point where the reed contact barely touches the flexible contact at the extremities of the swing of the reed. The conventional arrangement is unsatisfactory because the electrical contact between the paths is not very forcefully made, and a little wiping action occurs. Oxide and other films may thus rapidly degrade the contact performance. Further, the length of the electrical contact interval becomes critically dependent on the amplitude of reed vibration, which in turn depends strongly on the driving voltage as well as other factors, particularly temperature and aging. Such a contact adjustment is thus poor in stability. A slight decrease in energizing voltage will reduce the amplitude of reed vibration to a point where no electrical contact at all can be made. Still further, the electrical contact adjustment is very critical.

Accordingly, it is an object of the present invention to provide a vibrating reed type switch capable of obtaining stable, short duration electrical contacts.

Another object of the present invention is to provide a vibrating reed type switch which provides stable operation independently of excitation voltage.

A more specific object of the present invention is to provide a vibrating reed type switch having the controlled vaniable connected across the flexible contacts which are relatively stationary with respect to the vibrating reed contact.

Patented July 30, 1963 A more general object of the present invention is to provide momentary periodic electrical contact apparatus for determining the amplitude of an alternating current signal during periodic intervals.

Another object of the present invention is to provide momentary periodic electrical contact apparatus comprising two vibrating reed type switches in which the resonant frequencies of the reeds are deliberately made to differ from each other and in which damping may be intentionally added with a driving coil arrangement energized from a common single phase power source.

Another object of the present invention is to provide momentary periodic electrical contact apparatus for detection of amplitude or phase modulated carriers, aflording nearly ripple free output and affording response time of substantially less than a cycle.

Further objects and advantages of the present invention will be readily apparent from the following detailed description taken in conjunction with the drawings in which:

FIGURES 1, 2A and 2B are schematic diagrams illustrating the manner in which my invention obtains the desired results;

FIG. 3 is an electrical schematic diagram of an illustrative embodiment of the invention; and

FIG. 4 [l5 an electrical schematic diagram of an alternate embodiment of the invention.

A chopper or vibrating reed type switch is illustrated in FIG. 1. A vibrating reed 2 having an armature 4 mounted at one extremity thereof and stationarily aflixed at the opposite end in an insulator 6 is driven by an electromagnet 8 by means of an alternating current excitation applied to the excitation winding 18. Electrical connections are made at the terminals 12, 14- and 16. Terminals 12 and 16 are connected to flexible contacts shown as adjusting screws 18 and 28, respectively. The reed 2 vibrates as a cantilever beam in the usual manner.

To overcome the disadvantages of the conventional arrangements, the contact screws 18 and 20 are adjusted toward the reed 2 to make each screw touch the reed for slightly more than half the time of the cycle of reed motion. There will then be a short interval, equal in duration to the excess of the contact time over half the period of reed vibration, during which both screws touch the reed, and there is thus during this time an electrical contact between the two screw contacts 18 and 20. Electrical contact is established when the reed 2 goes through its neutral position, rather than at the extremities of its swing as in conventional arrangements.

With an arrangement as illustrated, electrical contact is established between the flexible contacts 18 and 20 in a forceful manner and considerable Wiping occurs. The neutral position of the reed 2 is independent of the excitation voltage and thus electrical contact is always made between the flexible contacts 18 and 20 as the vibrating reed contact 2 goes through its neutral position, regardless of the excitation voltage. It can be seen, with such an arrangement that a small percentage decrease of reed vibration amplitude will cause roughly the same percentage increase in the duration of the momentary electrical contact between the flexible contacts 18 and 20, whereas in the conventional arrangement it would cause a very large percentage decrease in electrical contact duration and it is even possible that no electrical contact would be made at all. A further advantage of connecting the variable alternating current signal across the flexible contacts 18 and 20 is that since the instance of electrical contact occurs when the vibrating reed contact 2 is traveling at its maximum velocity, the time of electrical contact is much less sensitive to the adjustment of the flexible contacts. Therefore, it is much easier to adjust the flexible contacts for a given duration of electrical contact than in conventional arrangements. Alternatively, a given accuracy of contact adjustment results in a much more accurately determined electrical contact time duration than in conventional arrangements. Of primary interest is the ability of such a vibrating type switch to have a positive electrical contact of extremely short time duration.

The vibrating reed type switch as shown in FIG. 1 differs in another respect from that of the conventional arrangement in that the switch makes a single pole, single throw type of electrical contact twice per cycle, whereas a conventional vibrating reed type switch makes a single pole, double throw type of contact to alternate circuits, each contact once per cycle.

Referring to FIG. 2A, wherein is shown a series combination of two single pole, single throw momentary contact vibrating reed type switches, as shown in FIG. 1; but with different driving excitation frequencies for the vibrating reeds, will provide a series electrical contact which is effectively closed only when both sets of flexible contacts are simultaneously closed. This will occur when each vibrating reed 2 is in its neutral position; thus providing a closed circuit between contacts a or b and d. the two driving frequencies are commensurable, this event will recur periodically, in general at a frequency equal to the greatest common divisor of the driving frequencies.

A single pole, single throw type of electrical contact once per cycle, retaining the advantages of the vibrating reed type switch shown in FIG. 1, can be realized by adding to such a switch a second vibrating reed type switch, similar to that in FIG. 1 except that the screws are adjusted so that the flexible contacts 18 and 24} make electrical contact with the vibrating reed 2 during a large portion, but slightly less than all of the portion, of each half cycle of reed vibration. Such an arrangement is diagrammatically illustrated in FIG. 2B. The contacts 18 and 2%) for the second vibrating reed type switch need not be flexible since their adjustment is such that electrical contact is less than each half cycle of reed vibration.

Vibrating reed switch VRSl is adapted so that a momentary electrical contact between flexible contacts and d occurs as its vibrating reed passes through its neutral position. Vibrating reed switch VRSZ is so arranged that the vibrating reed e alternately makes contact with flexible contacts a and b on alternate halves of its motion but never makes simultaneous electrical contact with both flexible contacts a and b. The vibrating reeds of both switches are made to vibrate at the same frequency but their motions are chosen to be different in time phase by an appreciable angle, say 90. Thus when the reed of switch VRSZ is near an extremity of its swing, making contact with flexible contact a, the vibrating reed of VRSl goes through neutral, making momentary electrical contact between the flexible contacts 0 and d and thus effecting a momentary electrical contact between the flexible contact a and the flexible contact d. Half a cycle later the process is repeated, with flexible contact a replaced by flexible contact 11. Since the momentary contact between c and 11 may occur any time during the electrical contact interval of a and c, the durations of contacts a, c and b, c are not critical. Nor is the phase difference between the reed motions critical. The same is true during the contact interval of flexible contacts 11 and c on the next half cycle. The time of occurrence, and the duration, of electrical contact between flexible contacts a and d or between b and d is determined only by the operation of vibrating reed switch VRSl. This arrangement is thus seen to perform a single-pole double-throw type of electrical contact to alternate circuits While providing stable short duration electrical contact intervals.

The diagrammatical illustration of the manner in which the present invention obtains the desired results has been shown in FIG. 23 as employing two separate vibrating reed switches. It may be desirable, however, to combine both vibrating reed switches in a single unit, although this unit must still employ two separate vibrating reeds with A, two flexible contacts at each reed. Since the reed vibrations must be out of phase, the driving energies for the reeds may be supplied by separate driving coils acting on separate magnetic circuits, the coils being supplied with separate, externally produced, out of phase voltages.

A simpler arrangement for producing the out of phase reed vibrations follows. If the natural resonant frequency of a reed is made equal to the frequency of the impressed driving voltage, the reed motion is in phase quadrature with the driving force, which in turn is in phase with the coil current. Suppose, however, that the resonant frequency of the reed were decreased in a manner such as adding mass to the reed. Since there is always some damping of the reed motion, the decrease of reed resonant frequency will result in a phase lag greater than between reed vibrations and driving force. Similarly, an increase of reed resonant frequency will cause the reed vibration to lag the driving force by less than 90 in phase. If now the two vibrating reed switches are combined in a single unit of such design that the two reed resonant frequencies are unequal, the reed vibrations will be different in phase when the driving forces of each reed are of the same phase, and thus a single driving coil and magnetic circuit, energized by a single periodic applied voltage, can drive both reeds with differing phases. A particularly attractive arrangement is to have the resonant frequencies of the reeds so adjusted that the reed motion for VRSZ lags the driving force by approximately 90 while that for VRSl is in phase with the driving force.

It may be desirable to add some damping to the reeds, in order to make the dependence of phase on driving frequency not too rapid; otherwise, the phases of the reed motions might be too sensitive to changes in driving frequency. The overall arrangement just described results in a single unit, driven by a single periodic excitation voltage source, which makes momentary electrical contacts of a single-phase, double-throw type, of highly precise and stable time of electrical contact initiation and of electrical contact duration.

The illustrative embodiment shown in FIG. 3 utilizes the connection of two vibrating reed switches VRSl and VRSZ in a manner diagrammatically shown in FIG. 2. The apparatus of FIG. 3 is capable of measuring the amplitude of a periodic voltage which amplitude depends on a quantity which it is desired to measure. Thus, an alternating current signal may be designated as f(t)P(t) where P(t) is a periodic function, of fundamental frequency S, and f(t) is the quantity to be measured, which may vary with time but should not vary too greatly during a time equal to the period 1/8 of the function P(t).

In radio transmission parlance, P0) is the carrier, and f(t) is the intelligence modulated thereon. The conventional manner of recovering f(t) is to rectify the output f(t)P(t), producing thereby a voltage containing a direct current component proportional to f(t), and containing also in general the fundamental and several harmonics of P(t). Often it is necessary to remove these alternating components of frequencies of S and higher which is done by a selective filter. Unfortunately, if the filter adequately removes harmonics, the response of its output voltage to the change in f(t) necessarily requires a time large compared to 1/5, the length of a cycle P0). In many cases it is necessary to have not only very low ripple content in the output, but also very rapid response to changes in f(t). Perhaps a delay of less than one carrier cycle is desirable. Such requirements are incompatible with a conventional system.

The electrical schematic diagram shown in FIG. 3 illustrates apparatus for solving this problem by making a momentary measurement, during a time interval short compared to 1/ S, of the alternating voltage f(t)P(t). prefer-ably at some point in the cycle where P is nearly amaximum.

Referring to FIG. 3 it can be seen that the two vibrating reed switches VRSl and VRSZ are connected in the same manner as. previously discussed with regard to FIG. 2. The excitation means for driving each vibrating reed e and comprises electromagnets M1 and M2, respectively, energized through phase shifters PS1 and PS2 from an excitation source indicated as terminals E.

The alternating current signal f(t)P(t) is connected to input means herein shown as input terminals I leading to an iron core transformer T having wound thereon a primary winding and a center tapped secondary winding. The center rap is connected to a reference point herein shown to be ground potential. Effectively appearing across the secondary winding of the transformer T are two signals 180 out of phase with each other and which signals alternately appear connected in series circuit relationship with the vibrating reed switches VRSI and VRSZ and energy storage means, herein shown to be a capacitor C connected between the flexible contact d and the reference point or ground. Output means, in the form of out put terminals 0, is connected across the energy storage means C to provide means for measuring the voltage across the capacitor and hence obtaining a measurement of the amplitude of the alternating current signal (t)P(t) appearing at the input terminals I.

As previously stated, FIG. 3 illustrates apparatus for making a momentary measurement, during a time interval short compared to 1/ S, of the alternating voltage f(t)P(t) preferably at some point in the cycle where P is nearly a maximum. The result of this measurement is stored as charge on the condenser C until a subsequent time, later by 'a full cycle of P(t) or perhaps less, at which time P(t) has the same value as it had at the previous time. The value of f(t)P(t) is then measured again, and the charge on the capacitor C is changed to the new value of f(t)P(t) which may diflfer from the earlier value. The amplitude of the component -P(t) is chosen to be of unitary value. The momentary measurement is made by connecting a suitable condenser C to the voltage f(t)P(t) during the desired time intervals by the momentary contact vibrating reed switch apparatus illustrated in FIG. 3. The switches VRSl and VRSZ are preferably energized by voltage of the same frequency as P(t) but a multiple or sub-multiple of this frequency may be used, and of fixed and properly chosen phase relation to P(t). The frequency and phase of -P(t) must thus be known for proper selection of the excitation voltages.

The measuring intervals may conveniently be made to coincide with every peak, alternately positive and negative, of P(t) as shown by the circuit arrangement in FIG. 3. If it is desirable to have a measuring interval coinciding with successive positive or negative peaks only of P(t) the circuit may be broken so as to disconnect the flexible contact a of the vibrating reed switch VRSZ from the end connection of the secondary win-ding of the transformer.

With more complicated arrangements any desired number of measurements per cycle may be made. It is evident from the foregoing that for 7"(1) constant, the condenser charge and voltage is constant and proportional to f(t); if a step change is made in f(t) a corresponding step change is made in the condenser voltage as soon as the next measuring interval occurs. The condenser voltage appearing across the output terminals 0 follows 1"(t) with a time lag no longer than the interval between successive measurements, but in spite of this short delay time the condenser voltage is nearly ripple free, a result not obtainable with the common rectifier and filter arrangements well known in the art.

Reference has heretofore been made only to amplitude modulator carriers. Phase modulated carriers may also be conveniently handled with the present invention if the degree of phase modulation is not too great. Consider a phase-modulated wave sin [wt+f(t)] where sin out is the calrier and 7(t) the modulating function. If a vibrating reed switch is so adjusted that the aforementioned measurements are made at time such that wt=2mr, where n runs through all the integers, then every measurement, one each cycle, is one of sin (t)], which nearly equals f(t) for small values of f(t). With the double-throw arrangement, measurements can be made for wt=mr, thus measuring (t) twice per cycle.

FIG. 4 illustrates an alternate embodiment utilizing a vibrating reed switch VRSZ similar to that illustrated in FIG. 3. A second vibrating reed switch VRS3 is illustrated which has its flexible contacts adjusted to close slightly less than half the cycle of its vibrating reed. Hence, a short duration open circuit may be made between the flexible contacts g and h otherwise connected by the vibrating reed 2'. In consideration of the known duality of electrical circuits, the discussion of FIG. 3 could be repeated for FIG. 4. All components similarly functioning are designated with the same reference characters as given in FIG. 3. In accordance with the duality of electrical circuits wherein currents are replaced by voltages, condenser by inductance, and short circuit by open circuit, apparatus is provided to recover a function f(t) from a current signal f(t)P(t). The current would be allowed to flow into a parallel combination of a suitable energy storage device herein illustrated as an inductance IND and a vibrating reed switch VRSZ to produce momentary open circuits across the inductance IND, short circuiting the inductance IND for the remainder of the operating time. In analogy to the previously discussed condenser storage of FIG. 3, the inductance current would be constant during short circuit at the value established at the previous momentary open circuit, changing as required to the new value at the next open circuit. This inductance may usefully be a control winding of a magnetic amplifier or other suitable device.

It is now readily apparent that the illustrative embodiments shown in FIGS. 3 and 4 are applicable to phase demodulation as well as amplitude demodulation. More complex arrangements for more measurements per cycle are possible, and the selection of excitation voltages driving the vibrating reeds and their frequency and phase 'angle relation to each other as well as the periodic signal voltage or current to be measured would apply in any selected case. The stability of the time of occurrence of the measurement interval is of paramount interest in any case.

While the present invention has been described with a particular degree of exactness for the purposes of illustration, it is to be understood that all alterations, equivalents, and modifications within the spirit and scope of the present invention are herein meant to be included.

I claim as my invention:

1. In combination, a plurality of vibrating reed type switches each comprising a vibrating reed contact and a set of flexible contacts, means for applying an alternating current signal in series with said flexible contacts, means for magnetically driving each reed contact into vibration at different frequencies, said flexible contacts of each said switch being adjusted to make electrical contact together for a time duration slightly longer than half the time of its associated reed contact vibration period, each said vibrating reed contact altering the continuity of said alternating current signal across is associated set of flexible contacts as the reed contact goes through its neutral position, said plurality of switches effecting short momentary changes in the continuity of said alternating current signal at a frequency equal to the greatest common divisor of the driving frequencies.

2. The momentary periodic electrical contact apparatus of claim 1 in which the driving frequency for said first vibrating reed contact is one-half of the driving frequency for the vibrating reed contact of the second switch.

3. Momentary periodic electric contact apparatus for determining the amplitude during periodic intervals of an alternating current signal having a predetermined frequency and phase angle comprising, in combination, a

first and a second vibrating reed type switch, said first and second switch comprising a first set of flexible contacts and a first vibrating reed contact and a second set of flexible contacts and a second vibrating reed contact respectively, circuit means for connecting said first set of flexible contacts, said second vibrating reed contact and one \Of said second set of flexible contacts in series circuit relationship, input means for applying said alternating current signal to said circuit means, means for magnetically driving each reed contact at a predetermined frequency and phase angle with respect to said alternating current signal, each flexible contact of said first switch making electrical contact with said first reed contact more than half the period of reed vibration, said second reed alternately making electrical contact with the flexible contacts of said second switch in alternate half cycles of its vibration, and output means connected to said circuit means for providing an output having a magnitude equal to the instantaneous magnitude of said alternating current signal whenever an electrical circuit is completed through said first and second switches.

4. Monetary periodic electric contact apparatus for determining the amplitude during periodic intervals of an alternating current signal having a perdetermined frequency and phase angle comprising, in combination, a first and a second vibrating reed type switch, said first and second switch comprising a first set of flexible contacts and a first vibrating reed contact and a second set of flexible contacts and a second vibrating reed contact respectively, circuit means for connecting said first set of flexible contacts, said second vibrating reed contact and one of said second set of flexible contacts in series circuit relationship, input means for applying said alternating current signal to said circuit means, means for magnetically driving each reed contact at the same frequency as said alternating current signal but out of phase to each other, each flexible contact of said first switch making electrical contact with said first reed contact more than half the period of vibration of said first reed contact, said second reed alternately making electrical contact with the flexible contacts of said second switch in alternate half cycles of its vibrations, and output means connected to said circuit means for providing an output having a magnitude equal to the instantaneous magnitude of said alternating current signal whenever a circuit is completely through said first and second switches.

5. Momentary periodic electrical contact apparatus for determining the amplitude during periodic intervals of an alternating current signal having a predetermined frequency and phase angle comprising, in combination, a first and a second vibrating reed type switch, said first and second switches comprising a first set of flexible contacts and a first vibrating reed contact and a second set of flexible contacts and a second vibrating reed contact respectively, means for magnetically driving each said reed contact at a predetermined frequency of vibration, circuit means for connecting said first set of flexible contacts, said second vibrating reed contact, and one of said second set of flexible contacts in series circuit relationship when each said vibrating reed contact is in a predetermined position, input means for applying said alternating current signal to said circuit means, output means connected to said circuit means for providing an output whenever the position of each said vibrating reed contact is in its respective predetermined position thereby completing the series circuit relationship, said first vibrating reed type switch being disposed so that when its vibrating reed contact passes through its neutral position momentary electrical contact is made between its associated set of flexible contacts, said second vibrating reed type switch being disposed so that its vibrating reed contact alternately makes electrical contact with its associated flexible contacts on alternate half cycles of its vibrations.

6. The momentary periodic electrical contact apparatus of claim 5 wherein each vibrating reed contact is so selected that the vibrating reed contact of the second switch is in electrical contact with one of its associated flexible contacts at the same time that electrical contact is made between said first set of flexible contacts.

7. The momentary periodic electrical contact apparatus of claim 5 in which the vibrations of each said vibrating reed contact are degrees out of phase with each other.

8. Momentary periodic electric contact apparatus for determining the amplitude during periodic intervals of an alternating cur-rent signal having a predetermined frequency and phase angle comprising, in combination, a first and a second vibrating reed type switch, said first and second switch comprising a first set of flexible contacts and a first vibrating reed contact and a second set of flexible contacts and a second vibrating reed contact respectively, circuit means for connecting said first set of flexible contacts, said second vibrating reed contact and one of said second set of flexible contacts in series circuit relationship when each said vibrating reed contact is in a predetermined position, input means for applying said alternating current signal to said circuit means, means for magnetically driving each reed contact at a predetermined frequency and phase angle, each flexible contact of said first switch making electrical contact with said first reed contact more than half the time of a cycle of reed motion, said second reed contact alternately making electrical contact with the flexible contacts of said second switch in alternate half cycles of its vibrations, and output means connected to said circuit means for providing an output having a magnitude equal to the instantaneous magnitude of said alternating current signal whenever said vibrating reed contacts complete the electrical series circuit relationship, each said vibrating reed contact including means for varying the mass of said reed and hence the resonant frequency of said reed so that the vibrations of each vibrating reed contact will be different in phase to each other.

9. Momentary periodic electrical contact apparatus for determining the amplitude of an alternating current signal during periodic intervals comprising, in combination, a first and a second vibrating reed type switch, said first and second switch comprising a first set of flexible contacts and a first vibrating reed contact and a second set of flexible contacts and a second vibrating reed contact respectively, electrical storage means, circuit means for conecting said first set of flexible contacts, said second vibrating reed contacts, and one of said second set of flexible contacts in series circuit relationship with said electrical storage means when said flexible reed contacts are in predetermined positions, input means for applying said alternating current signal to said circuit means, said alternating current signal having a predetermined frequency, output means connected across said electrical energy storage means, each flexible contact of said first switch adapted to make electrical contact with said first vibrating reed contact more than half the period of its reed vibration, said second vibrating reed and said second set of flexible contacts disposed so that said second vibrating reed alternately makes electrical contact with the flexible contacts of said second switch in alternate half cycles of its variation, a series circuit connection being accomplished for an instant upon the simultaneous occurrence of the first vibrating reed contact being in its neutral position and the second vibrating reed contact being in its extended position making electrical contact with said one of the said second set of flexible contacts as determined by the simultaneous occurrence of maximum driving force on said second vibrating reed contact and minimum driving force on said first vibrating reed contact, the voltage across said energy storage means at each said instant being equal to the magnitude of said alternating current signal.

10. The momentary periodic electrical contact apparatus of claim 9 in which said input means comprises transformer means having a primary Winding and a secondary winding with the secondary winding serially connected with one of said second set of flexible contacts for measuring successive peaks of a predetermined polarity of said alternating current signal.

11. The momentary periodic electrical contact apparatus of claim 9 in which said input means comprises transformer means having a primary winding and .a center tapped secondary winding, said second set of flexible contacts being connected to opposite ends of said secondary winding and said center tapped connection being connected to a reference for measuring successive peaks of either polarity of said alternating current signal.

12. Momentary periodic electrical contact apparatus for determining the amplitude of an alternating current signal during periodic interv als comprising, in combination, a first and a second vibrating reed type switch, said first and second switch comprising a first set of flexible contacts and a first vibrating reed contact and a second set of flexible contacts and :a second vibrating reed contact respectively, means for magnetically driving each said vibrating reed contact at individually selected frequencies and phase relationships to each other and said alternating current signal, each flexible contact of said first switch being disposed to make electrical contact with said first vibrating reed contact for a period more than half the period of its reedvibration, said second vibrating reed contact alternately making electrical contact with the flexible contacts of said second switch in alternate halt cycles of its vibration, circuit means for connecting each said switch in series circuit relationship upon the simultaneous occurrence of the making of electrical contact by each said vibrating reed contact, input means for applying said alternating current signal to said circuit means, electrical energy storage means operably connected to said circuit means, output means connected across said electrical energy storage means for providing an output whenever said vibrating reed contacts are simultaneously making electrical contact, the output of said output means having a magnitude related to the instantaneous magnitude of said alternating current signal at the moment simultaneous occurrence oi? the predetermined positions of each vibrating reed contact occurs.

References Cited in the tile of this patent UNITED STATES PATENTS 2,618,717 Westin Nov. 18, 1952 2,677,094 Kelley et al. Apr. 27, 1954 2,718,570 Caldwell Sept. 20, 1955 2,892,106 Giori June 23, 1959 FOREIGN PATENTS 886,941 France Oct. 28, 1943 904,695 France Nov. 13, 1945 1,031,888 Germany June 12, 1958 

1. IN COMBINATION, A PLURALITY OF VIBRATING REED TYPE SWITCHES EACH COMPRISING A VIBRATING REED CONTACT AND A SET OF FLEXIBLE CONTACTS, MEANS FOR APPLYING AN ALTERNATING CURRENT SIGNAL IN SERIES WITH SAID FLEXIBLE CONTACTS, MEANS FOR MAGNETICALLY DRIVING EACH REED CONTACT INTO VIBRATION AT DIFFERENT FREQUENCIES, SAID FLEXIBLE CONTACTS OF EACH SAID SWITCH BEING ADJUSTED TO MAKE ELECTRICAL CONTACT TOGETHER FOR A TIME DURATION SLIGHTLY LONGER THAN HALF THE TIME OF ITS ASSOCIATED REED CONTACT VIBRATION PERIOD, EACH SAID VIBRATING REED CONTACT ALTERING THE CONTINUITY OF SAID ALTERNATING CURRENT SIGNAL ACROSS IS ASSOCIATED SET OF FLEXIBLE CONTACTS AS THE REED CONTACT GOES THROUGH ITS NEUTRAL POSITION, SAID PLURALITY OF SWITCHES EFFECTING SHORT MOMENTARY CHANGES IN THE CONTINUITY OF SAID ALTERNATING CURRENT SIGNAL AT A FREQUENCY EQUAL TO THE GREATEST COMMON DIVISOR OF THE DRIVING FREQUENCIES. 